1. Field of the Invention
The present invention relates to refrigeration systems. More specifically, the present invention relates to methods and apparatus for sealing refrigeration systems.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Freon is the refrigerant most frequently used in conventional refrigeration systems. Unfortunately, freon has been found to be detrimental to the atmosphere. That is, the chlorine in freon is currently believed to deplete the layer of ozone in the atmosphere. Thus, there is an ongoing effort to discover alternative approaches to the use of freon for air conditioning and refrigeration systems.
Reverse Stirling cycle refrigeration systems provide a promising alternative to conventional freon based systems. Currently for cooling infrared sensors, reverse Stirling cycle cryogenic refrigerators are used. A typical unit consists of a compressor piston in a first cylinder, an expansion piston in a second cylinder, and a drive mechanism including a motor, a crankshaft, flywheel, and connecting rod connecting the crankshaft to each piston, a regenerator, and a crankcase housing. The drive mechanism converts the rotary motion of a motor via a crankshaft to a reciprocating motion of the two pistons with a 90 degree phase angle there between. The unit is filled with helium gas which serves as the working fluid. The out-of-phase motion of the two pistons allows the gas to be compressed, expanded, and moved back and forth between the cylinders without the need for valves.
In theory, helium in the compressor is compressed isothermally while rejecting heat to the surroundings. During this phase of the cycle, most of the gas is in the compressor and regenerator volumes. The gas is then forced through the regenerator by the motion of the displacer piston causing it to be cooled at constant volume. The heat removed from the gas is stored in the regenerator. Cold gas from the regenerator is next expanded isothermally while absorbing heat from the low temperature source. The gas is then forced back through the regenerator where it is heated at constant volume. The energy stored in the regenerator is now transferred back to the gas.
Unfortunately, helium, as a working fluid, is difficult to seal. For certain applications, this is particularly problematic. For example, automotive air conditioning systems are typically designed for a 10 year life (100,000 miles). However, these systems are typically not used for 98% of the useful life thereof. This results to 3,000 hours of life as opposed to the designed life of 10 years. Hence, fluid leakage is a significant problem for both conventional/freon as well as the Stirling/helium air conditioning systems.
The leakage is due, at least in part, to the failure of dynamic seals about the rotating shaft of the compressor. A typical dynamic seal for a rotating shaft is either a "lip seal" or a "face seal". As these types of seals have to seal against a rotating surface in order to allow the relative motion, the seal can not be tightly held against the shaft. Consequently, a small leak will occur and will get worse after the seal is worn. In the automotive air conditioner, the leakage occurs from such damaged and worn dynamic seals.
Thus, there is a need in the art for an improvement in the sealing systems of conventional and Stirling cycle cryogenic refrigeration and air conditioning systems.